MK-484 TRF AM RADIO Chip in TO-92 Pack

The MK484 is an offshoot of the famous Ferranti ZN-414 and is a tuned radio frequency (TRF) radio in a small TO-92 transistor-like package. Combined with (these parts not included) three resistors, three capacitors, an ear phone, 1.5V battery, tuning coil and tuning capacitor, you can make an AM receiver for the AM band and up to 3 MHz. See our article in the July issue of our newsletter for a circuit example with details. Suggested schematic and parts list sent with each IC (chip). See Cat # XSMK. $2.49 each.

Alligator Clip Five Pack

This "five" pack includes five alligator clips. each 2 inches in length. As per the picture, each clip has a screw terminal for attaching a wire. Ideal for clipping leads to coils or making up jumper cables.

Binder Post, Brass

Small brass connector post similar to those used in early radios. Includes custom threaded 0.15 inch diameter base screw and thumb wheel top for tightening wire. Wire opening is 0.1 inch and accommodates old style headphone plug terminals.

Detector Parts

The picture below displays additional brass parts and a compression spring. These parts are used in our Galena Detector Kit and are useful for other projects too. The 1.5 inch free-length, 0.3 dia spring is shown at left. A 0.375-inch 6-32 taped brass ball is second to left. These two parts can be mounted on the 2.5-inch threaded rod noted above. The rod we stock is brass. The next item is the brass cup, which accepts our Mounted Galena (see further down the parts page). The cup contains two 4-40 holes for mounting and securing the Mounted Galena. The L-Bracket, two of which can be used to hold the rod and ball in a detector assembly, is shown at right. (see the Galena Detector Kit picture).

Capacitor, 365 air variable

As the surplus for 365pf caps has dried up, these little beauties were getting harder and harder to find. Not anymore! The Society now has a plentiful supply; we have them manufactured. They are brand new caps, 31 blade, .010-air-gap, 1/4" tuning shaft, and CW rotation decreases capacitance. Testing indicates a capacity range of 390 (fully meshed) to 16 pf (fully open). Shaft accommodates the point knob shown (sold separately), and a reduction drive for slower tuning (also sold separately).

Connections. The frame of the capacitor is connected to the rotor plates and electrical connection must be via a solder lug (or other arrangement) with a 6-32 screw in the bottom, front, or back of the frame. (The 1920s units were this way!). The fixed plates connect to any of the solder lugs installed in the little brown phenolic boards on each side.

The cap can be panel mounted from the front or on its base via pre-taped 6-32 holes. The spacer shown (and sold separately) enhances mounting the cap via its base. Without a shim or spacer, the phenolic connector boards at each side may be broken when tightening the mounting screws. The spacer fits between the phenolic (pcb) legs and matches up with the holes in the bottom of the cap. Machine screws must be 6-32 by 3/8ths or ¼-inch, depending upon the thickness of the mounting surface. (Screws are not provided.)

Capacitor, 365 air variable with 8:1 reduction drive shaft

This variable cap is exactly like our 365 listed above but includes an 8:1 reduction drive, embedded in the shaft. It's part number is 365-8-1.

What's a reduction drive? It's a mechanical device wherein the plates of the capacitor turn at a slower rate than the attached knob. With this assembly it takes four rotations of the knob to turn the 365 cap from max to min capacitance. Thus a very small change in capacitance is easier to tune/achieve.

Electrical Connections. The frame of the capacitor is connected to the rotor plates and electrical connection must be via a solder lug (or other arrangement) with a 6-32 screw in the bottom or side of the frame. Solder lugs connect to the stator via the brown phenolic plates. The spacer listed above fits the 365-8-1 too.

Capacitor, Dual Gang air variable

The 1/4-inch shaft rotates both sections of rotary plates simultaneously, and each is grounded to the general case - and is thus a common connection point via the frame with screws/lugs. Each section of stationary plates is isolated and has separate solder lugs and mica trimmers. Mounting is with 6-32 machine screws via dimpled standoff holes on the bottom of the chassis.

Planetary Reduction Drive, 6:1

This add-on reduction drive rotates the shaft of an attached device - such as our 365 capacitor - at 1/6-th the turning rate of the front panel knob. The shaft of the driven device is secured by set-screws in the enlarged output shaft of the drive, and the drive is mounted with an L-bracket via the two "wings" as shown in the picture. The input shaft accommodates a 1/4-inch knob.

This drive can be combined with our 365-8-1 capacitor for a gigantic reduction in cap plate rotation of 48:1!

Mounting Bracket for the Planetary Reduction Drive

As per requests from the membership, we have modified the mounting bracket for the RD 6-1 reduction drive to mate with the 365 dual-gang cap as well as with the 365 and 365 8:1caps. As noted in the picture, the “RD2 Bracket” is L-shaped, secures at the base with 4-40 or 6-32 hardware, and attaches to the reduction drive with 4-40 nuts and machine screws. (The nuts and screws are not provided.) The large opening in the center accommodates the large shaft of the drive, which in turn slips over a ¼-inch tuning shaft of the XSS-365 capacitors or other components such as panel mount pots. For the RD2 Bracket to fit with the XSS-365 capacitor, it is assumed that the 0.060-inch capacitor mounting "spacer," or two solder lugs are placed under the cap. (See the XSS-365).

Capacitor assortment

This ceramic cap assorment includes two each of caps commonly found in crystal sets, as per the table. A sheet on how to identify labeling on the capacitors comes with the assortment.

Catwhisker, Phospher Bronze

Small wire with wound springy end for "catwhisker" replacement in a detector stand. Generally one screws the wound (springy) portion of the whisker onto a threaded shaft. The other end is pressed against a mineral, such as galena.

Coil Forms: Cylindrical and Toroidal

The PVC & ABS plastic pipe forms - cylindrical - are pre-cut and pre-drilled, ready for you to wind coils. Each kit contains 3 pipes, 6@ 6-32 metal screws and 6 nuts, and a coil information sheet. You may wish to use nylon (non-conducting) nuts & bolts to install the forms in a set. See Nylon-Parts. Also see the Coil Calculator to determine number of turns for a target inductance. As with wood, actual diameter of pipe is not the same as that called out or printed on the pipe. Physical outside diameter and length for each form is listed below.

The Toroidal Coil form kit includes two FT-82-61 ferrite toroids with nylon washers and nylon machine screws/bolts for mounting and instructions for winding enamel wire. These ferrites are ideal for the AM Broadcast Band. We recommend #26 magnet wire, not included.

Diodes, 1N34:    The 1N34 has radial leads and a glass housing. Dark ring on one end denotes the "negative" side.

Earplug, Crystal

High impedance crystal earphone with tinned ends. Use in place of old-style hi-impedance headphones. Place a 47K or greater resistor across the earplug leads.

Fahnestock clips:   Used to connect antenna, earplug, or phones to a set. Fits 6-32 nut and screw (not provided).

Galena Crystals

We offer galena crystals in a 0.475 inch diameter woods metal mounting or raw. Each mounted crystal has been tested. The mounting fits nicely in many old style detector stands. Crumpled aluminum foil and a wire jammed into a hole can offer an alternative way of mounting.

Inductors, Miniature

Packs include 4 molded RF chokes (that look like resistors), suitable as coil substitutes for making miniature crystal sets. Just think; you can make crystal sets without winding a single coil. Q will be somewhat less than when using wire wound coils. Packs include a sheet on several possible projects to build. The L-Pack includes one each as in the table. The 250-pack includes 2 33 uH and 2 250 uH molded coils.

Knob, Pointer

This knob fits on a ¼-inch shaft; hence, it fits our 365 single and dual gang air capacitors and panel mount pots. Set screw in knob secures knob to shaft. The knob is shown in the picture with the 365 air variable capacitor above.

Potentiometers, panel mount

These potentiometers are ideal for front panel installation. Both log and linear taper 10K, 100K, and 1MEG pots are now stocked. Log taper are ideal for audio volume control and linear taper are useful for diode bias or a Benny, amoung other apps. Pots include three solder lug terminals, 0.25" dia by 0.5" (in front of panel) shaft with threaded base, tit, and nut for mounting, and fit our pointer knob too!

Resistor, 47K:   This 1/4-watt resistor is sued with our earplug in a number of kits, including the Oat Box Kit.

Solder Lugs:   Useful for may connections, including chassis ground. Mounts with 6-32 nuts and screws (not included).

Toroid, FT-82-61

Ferrite toroids are often used as a form for winding a coil, enabling a large inductance in a small space. The FT-82-61 is suitable for the AM broadcast band and hence for crystal sets. For a desired inductance, the number of turns required is calculated as follows:

For the FT-82-81, N (# turns) = 1000*SQRT(L(in mH)/73.3). Hence 58 turns provides for an L of 250 uH. The equation varies for different sizes and types of ferrite materials.

Toroidal coils can be mounted using glue or nylon washers and screws, not included.

We also sell this toroid in a TWO PACK KIT, including nylon hardware, as noted at right in the picture. The toroid is mounted between two large 1.25 inch nylon washers, which in turn are secured by a nylon hex nut. The nut is 2 inches long, enabling you to stand the toroid 1.5 inches above the mounting surface with the remaining two nuts. The coil leads then drape down and are attached to whatever.

Transformer: 1200-to-8 ohm

This transformer is useful as part of a matching network for a crystal set to 8-ohm headset or speaker. Primary is 1200 ohms; secondary is 8 ohms. Application sheet included. For sensitive (DX) sets, one must use an intermediate transformer between the set and this transformer. For beginner sets, try tapping the detector diode part way down the set coil and interconnect the other end of the diode to the primary of this transformer. An 8-ohm headset would then be attached to the secondary 8-ohm output.

Wire: hookup, magnet & Litz:   Coils can be wound with hookup, magnet, or Litz wire. See the January 2008 issue of the Xtal Set Society Newsletter for an introduction to the use of Litz (or woven) wire. Wire diameter and covering are listed in the table.